1. Field of the Invention
Apparatuses consistent with the present invention relate to a multi-loop type transformer, and more particularly, to a multi-loop type transformer capable of enhancing efficiency of a power amplifier by reducing power loss.
2. Description of the Related Art
In general, wireless communication equipment such as a handheld terminal employs semiconductor chip devices having radio frequency communication circuits built therein. Out of the chip devices, it is very important in terms of material cost reduction and transmitter efficiency to built as one single chip a transmitter and a high-frequency power amplifier having an appropriate power level. To build such a single chip, the power amplifier should be built with CMOS devices like the transmitter built with the CMOS devices. The CMOS device has difficulties in building the power amplifier since it has low breakdown voltage and substrate resistance. The technologies building a power amplifier overcoming such a low breakdown voltage and substrate resistance should be inevitably achieved for higher power output and efficiency improvement of integrated-circuit amplifier.
The distributed active transformer (DAT) is used to increase such a breakdown voltage of the power amplifier.
FIG. 1 is a circuit diagram for showing a conventional DAT. As shown in FIG. 1, the DAT has a first loop 10 to which electric power is supplied, second loop 20 generating induction current by current flowing in the first loop 10, and plural power supply units 60 for supplying power to the first loop 10.
The first loop 10 is formed with four metal plates disposed to be formed in a rectangular shape, and each metal plate serves as a drain tuning inductor for resonating the transistor parasitic capacitance and controlling a harmonic signal. Here, the metal plate inductor shows a higher Quality factor (Q-factor) than a spiral inductor.
Power supply units 60 are disposed between neighboring metal plates, and each interconnects the cathode terminals of output ports of the neighboring metal plates. Each power supply unit 60 is formed with a pair of transistors the sources of which are connected with each other and commonly grounded. One of the transistors is driven when its gate is supplied with a positive phase signal, and the other transistor is driven when its gate is supplied with a negative phase signal. Such power supply unit 60 causes each corner of the first loop 10 to be substantially AC-grounded.
The second loop 20 is formed with a metal plate of a rectangular frame shape forming one loop, and each side of the metal plate serves as one metal coil. That is, the second loop 20 generate induction current by the first loop 10 and serve as the second loop of the transformer.
The loss of such a DAT affects the efficiency of the whole module of a power amplifier, and, in particular, the DAT has a drawback of degrading the efficiency of the whole power amplifier when used as an output matching circuit of the power amplifier, since the loss of the DAT itself is large.
In general, the loss of the DAT becomes smaller as the metal plates forming the first loop 10 and the second loop 20 become thicker or as the virtual centers of the first loop 10 and the second loop 20 become closer. Here, the virtual center refers to a substantial center line of a magnetic field occurring when current flows in the first loop 10 and the second loop 20. Since the first loop 10 and the second loop 20 of the conventional DAT are a single loop respectively, the center line of the first and second loops 10 and 20 becomes a line connecting the centers in the traverse direction of the metal plates forming a loop.
However, in general, the thickness of a metal plate forming a loop of the DAT is determined at the time of a production process, and the current DAT structure having a single first loop 10 and a single second loop 20 causes the virtual centers of the respective loops to be considerably spaced apart.
Therefore, instead of thickening the thickness of the metal plate of the DAT, an approach is sought to compensate for the thickness and an approach is sought to shorten a distance between the virtual centers between the first loop 10 and the second loop 20, so the loss of the DAT is reduced to improve the efficiency of the power amplifier